USLEを用いたエチオピア国東ショワ地域における土壌侵食の評価

エチオピア国では山林の伐採および耕作区域の拡大のため,土壌侵食による国土の荒廃が著しく,人々の生活を脅かす深刻な問題となっている。実際に,土壌侵食に伴う土壌栄養分の減少,干ばつおよび飢饉がエチオピアで頻繁に起こっている。生産性の高い表土のほとんどは侵食作用で削り取られ,結果として慢性の食糧不足および回復の困難な貧困がつづいている。土壌侵食は,エチオピア国において農業の持続性を脅かす重要な環境問題である。本研究の目的は,エチオピア国オロミア地域の東ショワ地帯を対象として,土壌流亡予測式(USLE)と地理情報システム(GIS)を統合することにより,広域的な土壌侵食の危険性を明らかにすることである。降雨量,地形,土壌および土地利用データをUSGSおよびエチオピア政府から入手し,GISを使用して広域データベースを作成した。その結果,侵食の程度が高い,非常に高い,著しい,非常に著しいと分類された面積が対象地域の74 %に上ることが明らかになった。それらの地域は北東地域,中央部及びと南部に分布し,主に耕作が繰り返されている土地や,家畜の放牧にさらされる潅木地と草原であった。

Landscape degradation by soil erosion has increased considerably in Ethiopian lands due to deforestation of natural mountain forests and the cultivation of large areas, resulting in a serious threat to the Ethiopian population. In fact, soil erosion and nutrient depletion, drought and famine have frequently occurred in Ethiopia. Most of the productive topsoil has been degraded, resulting in chronic food shortage and persistent poverty. Soil erosion is a major environmental problem threatening the sustainability of agriculture. The purpose of this study is to establish spatial information of soil erosion risk at East Shewa Zone, Oromia Region in Ethiopia by conducting the integration of the Universal Soil Loss Equation (USLE) using Geographic Information System. Precipitation, topographic, soil data, and land use data were obtained from USGS records and from Ethiopian governmental offices and put into a spatial database using GIS. The factors that influence soil erosion are rainfall erosivitiy (R) obtained from the precipitation database, soil erodibility (K) obtained from the soil database, slope length and steepness (LS) obtained from the topographic database, while crop and management (C) and conservation supporting practices (P) were obtained from the land use database. The erosion analysis through USLE applied on GIS show that most of the lands is East Shewa zone (82%) are under high, very high, severe or very severe erosion and are covered mainly by cultivation, shrublands and grasslands. These lands essentially prone to erosion are located mostly in the northeast, center and south-west of the study area. This study presents the evidence for erosive areas repeatedly cultivated or frequently suggested for grazing such as shrublands and grasslands as is the case of most areas in East Shewa.

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KJ00007059040

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